US4696057A - CN ratio measurement circuit - Google Patents

CN ratio measurement circuit Download PDF

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Publication number
US4696057A
US4696057A US06/787,422 US78742285A US4696057A US 4696057 A US4696057 A US 4696057A US 78742285 A US78742285 A US 78742285A US 4696057 A US4696057 A US 4696057A
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circuit
output
branching
signal
averaging
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US06/787,422
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English (en)
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Susumu Otani
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NEC Corp
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NEC Corp
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R29/00—Arrangements for measuring or indicating electric quantities not covered by groups G01R19/00 - G01R27/00
    • G01R29/26—Measuring noise figure; Measuring signal-to-noise ratio

Definitions

  • the present invention generally relates to a time division multiple access (TDMA) communication system and, more particularly, to a circuit for measuring carrier power to noise power ratio in a TDMA transmission channel in which a nonlinear signal processing element exists.
  • TDMA time division multiple access
  • TDMA communication systems utilizing satellites have come to be extensively used. Constant monitoring of the quality of a communication channel is of primary concern from the standpoint of channel maintenance and channel quality.
  • the carrier power to noise ratio is one of the items to be monitored for the above purpose and has heretofore been measured in the prior art by measuring carrier power and noise power with a power meter.
  • an object of the present invention to provide a CN ratio measurement circuit which is capable of measuring an accurate CN ratio even if a nonlinear signal processing element is present in a transmission channel.
  • a CN ratio measurement circuit includes a bandpass filter for band-limiting an input signal, a first branching circuit for branching an output of the bandpass filter to produce two outputs, a first ⁇ /2 phase shifter for rotating a phase of one of the two outputs of the first branching circuit by ⁇ /2 radians, and an amplitude-limiter for limiting an amplitude of an output of the first ⁇ /2 phase shifter, a second ⁇ /2 phase shifter for rotating a phase of an output of the amplitude-limiter by another ⁇ /2 radians.
  • the CN ratio measurement circuit further includes a second branching circuit for branching an output of the second ⁇ /2 phase shifter to produce two outputs, a delay circuit for delaying one of the two outputs of the second branching circuit, a third branching circuit for branching an output of the delay circuit to produce two outputs, a first multiplier for producing a product of one of the two outputs of the third branching circuit and the other output of the first branching circuit, a third ⁇ /2 phase shifter for rotating a phase of the other output of the third branching circuit by ⁇ /2 radians, a second multiplier for producing a product of an output of the third ⁇ /2 phase shifter and the other output of the second branching circuit.
  • the CN measurement circuit also includes a first averaging circuit for averaging an output of the first multiplier, a first squaring circuit for producing a square of an output of the first averaging circuit, a second squaring circuit for producing a square of an output of the second multiplier, a second averaging circuit for averaging an output of the second squaring circuit, a divider for dividing an output of the first squaring circuit by an output of the second averaging circuit, and a constant circuit for multiplying an output of the divider by a predetermined constant.
  • FIG. 1 is a block diagram modelling a satellite communication system
  • FIGS. 2A and 2B are diagrams demonstrating an occurrence that when in-phase noise and quadrature noise associated with a signal are passed through a nonlinear element, the in-phase noise is removed by the nonlinear element;
  • FIG. 3 is a block diagram of a CN measurement circuit embodying the present invention.
  • FIG. 4 is a block diagram showing in detail a logic processor which is included in the circuit of FIG. 3;
  • FIG. 5 is an exemplary timing chart representative of a case wherein an unmodulated portion is employed for measurement with the circuit of the present invention to be carried out in TDMA communication.
  • FIG. 1 models a satellite communication system.
  • the reference numeral 101 designates a transmit earth station, 102 a satellite transponder, and 103 a receive earth station.
  • Up-link noise is represented by N U and down-link noise by N D .
  • the true CN ratio should be C/(N U +N D ).
  • the satellite transponder 102 is generally implemented by a nonlinear element, perfect limiters being used with some communications satellites.
  • a major problem that results is that it is impossible to measure the up-link noise N U from an output of such a nonlinear element using a wattmeter. To demonstrate this, reference is made to FIGS. 2A and 2B.
  • input noise power N U is defined by in-phase noise n' c (t) and quadrature noise n' s (t) as n' c 2 (t)+n' s 2 (t), where () 2 indicates a mean square.
  • the in-phase noise n' c is removed by the nonlinear element and does not appear in an output of the element, that is, only n' s 2 (t) appears. For this reason, the prior art wattmeter scheme for CN ratio measurement fails to provide an accurate CN ratio when a nonlinear element is present in the transmission channel.
  • the CN measurement circuit comprises a bandpass filter 301, an amplitude-limiter 302, a delay circuit 303 for providing a delay time T, multipliers 304 and 305, ⁇ /2 phase shifters 306, 308 and 309, a logic processor 307, branching circuits 310, 311 and 312, a signal input terminal 350, and a CN output terminal 351.
  • the signal coming in through the input terminal 350 as shown in FIG. 3 is the sum of a signal s(t) and noise ni(t). Measurement of a CN ratio is generally performed during an unmodulated period such as the period of a word which precedes a TDMA burst signal for synchronization purpose, which will be described. With this in mind, the operation of the circuit of FIG. 3 will be described during an unmodulated portion in which s(t) is ⁇ 2P cos ⁇ o t, where P is a signal envelope and ⁇ o , an angular frequency of a signal.
  • the input signal propagates through the bandpass filter 301 whose center frequency is ⁇ o /2 ⁇ .
  • noise n(t) in the filter output may be expressed as
  • the output signal Dq(t) of the multiplier 304 is the product of the signal represented by the Eq. (3) and a signal provided by phase-rotating by ⁇ /2 the signal represented by the Eq. (4) by the ⁇ /2 phase shifter 306.
  • the logic processor 307 is made up of an averaging circuit 501, squaring circuits 502 and 503, an averaging circuit 504, a divider 505, a constant circuit 506, input terminals 520 and 521, and an output terminal 522.
  • the signal given by the Eq. (5) is applied to the input terminal 520.
  • the output signal of the squaring circuit 502 is:
  • the divider 505 divides the output of the squaring circuit 502 by the output of the averaging circuit 504, producing an output: ##EQU14##
  • TDMA burst signals 401 and 402 are shown in which are transmitted from TDMA earth stations.
  • a burst signal precedes a preword burst which is adapted for demodulator synchronization, so that a demodulator may be rapidly synchronized.
  • a desirable example of the synchronizing preword is an unmodulation.
  • CW in FIG. 5 represents an unmodulated signal. Since in a TDMA system the point of arrival of a received signal can be predicted, the circuit in accordance with the present invention is applicable to such a system by using a signal which occurs as indicated by the reference numeral 403 in FIG. 5.
  • the present invention provides a CN ratio measurement circuit which entails no error despite possible influence of a nonlinear element located in a transmission channel. This is because the present circuit measures noise power from only the noise which is orthogonal to a signal. Hence, even if a satellite transponder includes a nonlinear element, the TDMA communication system, even while the channel is in use, is capable of measuring an accurate CN ratio. This can be accomplished by furnishing a burst signal with an unmodulated portion and, sampling such unmodulated portions of burst signals to be measured.

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Monitoring And Testing Of Transmission In General (AREA)
  • Radio Relay Systems (AREA)
  • Mobile Radio Communication Systems (AREA)
US06/787,422 1984-10-16 1985-10-15 CN ratio measurement circuit Expired - Fee Related US4696057A (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
JP59-217047 1984-10-16
JP59217047A JPS6195635A (ja) 1984-10-16 1984-10-16 Ｃｎ比測定回路

Publications (1)

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US4696057A true US4696057A (en) 1987-09-22

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US06/787,422 Expired - Fee Related US4696057A (en) 1984-10-16 1985-10-15 CN ratio measurement circuit

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US (1) US4696057A (enrdf_load_stackoverflow)
EP (1) EP0181701B1 (enrdf_load_stackoverflow)
JP (1) JPS6195635A (enrdf_load_stackoverflow)
DE (1) DE3567283D1 (enrdf_load_stackoverflow)

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4940947A (en) * 1989-02-28 1990-07-10 Oneac Corporation Line noise signal measurement system using analog signal compression with digital linearity correction
WO1992017005A1 (en) * 1991-03-21 1992-10-01 Nokia Telecommunications Oy Method for identifying a supervising signal at a base station of a mobile telephone system
US5826198A (en) * 1992-01-13 1998-10-20 Microcom Systems, Inc. Transmission of data over a radio frequency channel
US6229847B1 (en) 1997-12-24 2001-05-08 The United States Of America As Represented By The Secretary Of The Navy Signal quality measurement device
US6982745B2 (en) * 2001-11-27 2006-01-03 Sony Corporation Antenna level display device and method, and receiving apparatus

Families Citing this family (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4845133A (en) * 1987-04-07 1989-07-04 The Dow Chemical Company Flexible polyurea or polyurea-polyurethane foams prepared from high equivalent weight amine-terminated compounds
JP3013408B2 (ja) * 1990-08-17 2000-02-28 ソニー株式会社 受信装置
DE4305961A1 (de) * 1993-02-26 1994-09-01 Nokia Deutschland Gmbh Anordnung zur Erzeugung eines Rauschdetektorsignals
JP5148792B2 (ja) * 2001-09-04 2013-02-20 アイシン精機株式会社 自動変速装置
JP3920816B2 (ja) * 2003-06-27 2007-05-30 日本無線株式会社 無線通信装置
JP4697593B2 (ja) * 2005-10-31 2011-06-08 住友金属工業株式会社 管内面の渦流探傷におけるｓ／ｎ比測定方法

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3350643A (en) * 1965-07-15 1967-10-31 James E Webb Signal-to-noise ratio estimating by taking ratio of mean and standard deviation of integrated signal samples
US4107608A (en) * 1975-12-10 1978-08-15 Nippon Electric Co., Ltd. Method and apparatus for burst synchronization in a time division multiple access communication system
US4553086A (en) * 1982-04-02 1985-11-12 Kokusai Denshin Denwa Kabushiki Kaisha Carrier power to noise power ratio measuring system for TDMA signals

Family Cites Families (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4408322A (en) * 1980-11-07 1983-10-04 Satellite Business Systems Method and apparatus for measuring signal to noise ratio in a TDMA communications system

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3350643A (en) * 1965-07-15 1967-10-31 James E Webb Signal-to-noise ratio estimating by taking ratio of mean and standard deviation of integrated signal samples
US4107608A (en) * 1975-12-10 1978-08-15 Nippon Electric Co., Ltd. Method and apparatus for burst synchronization in a time division multiple access communication system
US4553086A (en) * 1982-04-02 1985-11-12 Kokusai Denshin Denwa Kabushiki Kaisha Carrier power to noise power ratio measuring system for TDMA signals

Non-Patent Citations (2)

* Cited by examiner, † Cited by third party
Title
P. Hetrakul, "The Effect of Satellite Transponder Nonlinearities on the Performance of Binary PSK Systems" (49-55).
P. Hetrakul, The Effect of Satellite Transponder Nonlinearities on the Performance of Binary PSK Systems (49 55). *

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4940947A (en) * 1989-02-28 1990-07-10 Oneac Corporation Line noise signal measurement system using analog signal compression with digital linearity correction
WO1992017005A1 (en) * 1991-03-21 1992-10-01 Nokia Telecommunications Oy Method for identifying a supervising signal at a base station of a mobile telephone system
US5826198A (en) * 1992-01-13 1998-10-20 Microcom Systems, Inc. Transmission of data over a radio frequency channel
US6564071B1 (en) 1992-01-13 2003-05-13 Microcom Systems, Inc. Transmission of data over a radio frequency channel
US6229847B1 (en) 1997-12-24 2001-05-08 The United States Of America As Represented By The Secretary Of The Navy Signal quality measurement device
US6982745B2 (en) * 2001-11-27 2006-01-03 Sony Corporation Antenna level display device and method, and receiving apparatus

Also Published As

Publication number Publication date
EP0181701B1 (en) 1989-01-04
JPS6195635A (ja) 1986-05-14
EP0181701A1 (en) 1986-05-21
DE3567283D1 (en) 1989-02-09
JPH0423971B2 (enrdf_load_stackoverflow) 1992-04-23

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